A known example of a wave gear device is a unit type in which a wave gear mechanism is incorporated into a housing, such as those disclosed in Patent Documents 1 and 2. In the unit type wave gear devices disclosed in these patent documents, a silk hat type wave gear mechanism is incorporated within a housing configured from a first end plate and a second end plate disposed at the sides of the device's axial direction, and a cross roller bearing disposed between the end plates. An input shaft extending through the center of the device is rotatably supported at both ends respectively by the first end plate and the second end plate via ball bearings.
In the unit type wave gear devices disclosed in Patent Documents 1 and 2, a wave gear mechanism is concentrically incorporated on the inner side of a cross roller bearing. Consequently, the axial dimension of the device can be reduced, which is advantageous towards making the unit type wave gear device flatter. A multi-stage cross roller bearing is provided in Patent Document 3 as a cross roller bearing.